1. Field of the Invention
The present invention relates to an implantable composite prosthesis and method for limiting the incidence of acute postoperative adhesions and calcified scar formation embedded in the prosthesis that can result in a lifetime of post surgical complications and in particular post-operative complications in the field of visceral or parietal soft tissue repair surgery.
2. Background of the Invention
Post surgical adhesions include all non-anatomical fibrous connections accidentally induced by a surgical act during the normal process of cicatrization and may occur in all surgical disciplines regardless of the operation in question. Adhesions can provoke syndromes which can be classed principally as but not necessarily limited to chronic pain, occlusive syndromes, intestinal obstructions and female infertility. Therefore, it is evident that there is a need for a suitable method for preventing the adhesions, and the complications and patient discomfort associated with them.
One solution to reduce acute adhesion consists of separating adjacent internal bodily tissues by interposing a barrier or surgical mesh and barrier layer prosthesis so that during tissue regeneration following surgery no contact exists between the repaired tissue and surrounding organs or other tissue. However, the desired barrier effect of a non-absorbable barrier material can itself be the source of adhesions over the course of time as experienced with current composite prosthesis comprising a barrier made of expanded PTFE (Composix® EX Mesh, Davol/BARD®, Cranston, R.I.); and if it is an absorbable barrier, its absorption must be sufficiently non-inflammatory so as not to be a cicatrizant and cause adhesions itself. In the field of internal medical care, such as internal surgery, there is a need for tissue regeneration devices which may prevent complications such as adhesions in the post-operative healing period.
The approach of utilizing a barrier material is used in U.S. Pat. No. 5,002,551 which discloses a physical barrier formed of a knitted oxidized regenerated cellulose. The patent indicates that other physical barriers include silicone elastomers and absorbable gelatin films. Such physical barriers alone are not sufficient to reinforce the abdominal wall or to repair abdominal wall defects.
As recognized in the art, particularly for visceral and parietal surgery, but also in orthopedic or neurological surgery, the composite prosthesis must also have a certain mechanical strength and permanence allowing it to fulfill a lifetime function as an element of surgical reconstruction. Generally, the known prosthetic fabrics or meshes, particularly in the treatment of parietal insufficiencies, for example hernias, other eventrations and organ suspensions, afford additional mechanical strength to the surgical reconstruction. Most surgical mesh used in the art have the characteristic of being densely knitted and constructed of a monofilament fiber or multifilament yarn so as to present a significant number of very small interstices caused by the knots or loops of the mesh that increase surface area and promote tissue in-growth of scar tissue inside these interstices. Even though scar formation has a purpose in tissue healing, clinically calcified scar tissue is considered pathological and suboptimal to connective tissue that can support blood vessels and act like normal native tissue. Unfortunately, current surgical mesh is constructed of synthetic materials that react with normal tissue invoking a chronic inflammation response and calcified scar encapsulating the mesh prosthesis. It is for this reason that upon contact with the viscera for example, these fabrics promote adhesion which is a feature that limits their use at the so-called preperitoneal or retroperitoneal sites. With some patients the mesh has to be removed due to the complications of scar pathology. In certain procedures, including incisional and umbilical hernia repair and chest reconstruction, the prosthetic mesh may come into direct contact with the sensitive abdominal viscera, creating postoperative adhesions between the mesh and the intestine, potentially leading to intestinal fistulization.
Because of the shortcomings of a non-absorbable barrier or mesh only approach, various approaches to reducing the incidence of postoperative adhesions during healing or chronic scaring arising from the use of prosthetic mesh materials have been used. One traditional solution is to cover the prosthesis with peritoneum or other tissue, where available or adequate to close the defect, to form a biological barrier between the implant and the bowel. Another solution includes the placement of a physical barrier between the surgical site and the surrounding tissue where adhesions are most commonly encountered.
Absorbable combinations of a mesh and other materials or barriers, such as those disclosed in U.S. Pat. No. 4,840,626 and U.S. Pat. Pub. No. 2005/0283256, have been disclosed for use, however there are surgical situations that benefit from having a mesh prosthesis that is not totally absorbed and therefore adds strength to a wound area after it heals.
Barriers having multiple layers, one of which is porous, are disclosed in U.S. Pat. Nos. 5,508,036 and 5,480,436. These barriers are helpful, however there are additional benefits provided by the strength provided by a mesh fabric.
One approach to address the above problems is to combine the features of a non-absorbable mesh with an absorbable barrier sheet. Jenkins et al., “A Comparison of Prosthetic Materials Used to Repair Abdominal Wall Defects”, Surgery, Vol. 94, No. 2, August 1983, pg. 392-398, describes a technique of placing an absorbable gelatin film (Gelfilm®) between a piece of Marlex knitted polypropylene monofilament mesh and the abdominal viscera. U.S. Pat. No. 6,451,032 describes a multi-layer prosthesis with one embodiment comprising a mesh and a collagenous material. U.S. Pat. No. 5,593,441 discloses a prosthesis comprising a mesh and an absorbable barrier. However, with these solutions, either through initial contact with the wound, or contact once the barrier is absorbed into the body, the uncoated mesh material stimulates in-growth of scar tissue into and around the mesh. In this case, in-growth is defined as a growth of tissue to or into a fabric, mesh or similar device, connecting an artificial surface to living tissue, but not necessarily extending through it. This in-growth results in fibrotic tissue that, through the fibrotic healing process, is eventually reabsorbed by the body. As a result of this reabsorption, the fibrotic layer formed on the mesh contracts in the direction normal to the mesh and in the plane of the mesh. As the layers contract they pull the mesh with it, causing it to fold and buckle. The result is usually a hard and painful locus of tissue and implant which also increases the instance of adhesion with surrounding tissues.
Microscopic examination of tissue in-growth in both polyester and polypropylene mesh suggests it is the inflammatory potential of the mesh that promotes fibrosis along the plane of the mesh. Therefore, to reduce fibrosis, it is beneficial to reduce the in-growth and inflammatory potential of the mesh.
As opposed to in-growth in the knots or loops of the mesh, tissue through-growth is a healing method that can only be promoted by preventing scar tissue forming in the interstices and promoting connective tissue growth through much larger windows or openings in the mesh fabric. This continuous tissue connection extends through the fabric or mesh or other artificial surface from one living tissue to another. In the case of a mesh and barrier combination, through-growth is confined to tissue connections between adjacent points on the layer of tissue surgically attached to the mesh. Connective tissue through-growth, promoted by the plurality of the larger window pane design, or openings of the mesh, helps decrease the likelihood of infections by preventing microbe proliferation along the surface of densely woven or knitted mesh. Through-growth also does not have the detrimental effects of fibrotic healing related to in-growth. Through-growth supports angiogenesis and further fights infections.
Hydrogels are a material that has a reduced potential for inflammation, and therefore fibrosis, in a tissue. Hydrogels are uniquely biocompatible and contain large amounts of loosely bound water that is free to equilibrate in osmolarity and chemical composition with the surrounding tissue. This exchange of the hydrogel water with the surrounding tissue water makes prosthetics made from hydrogel more tissue-like and hydrophilic, and discourages the attachment of protein markers on the surface of the prosthetic. These features dramatically reduce the inflammatory potential of the prosthetic and reduce the promotion of fibrosis. However, hydrogel-based prosthetics are not currently used in surgical soft tissue repair, primarily because such prosthetics are expected to provide permanent tissue support and most hydrogels are either absorbable or possess little tensile strength.
U.S. Pat. No. 5,593,441 discloses a method for limiting the incidence of postoperative adhesions. A composite of a mesh and a barrier is positioned with the barrier facing away from the defect wall opening. The mesh has a plurality of interstices constructed and arranged to allow tissue in-growth.
U.S. Pat. Pub. No. 2006/0233852 discloses hydrogels reinforced with mesh for use in the repair of tissue defects such as a hernia in order to reduce the incidence of adhesions. The entire contents of U.S. Pat. Pub. No. 2006/0233852 is incorporated herein by reference as if repeated in full herein.